1. Field of the Invention
The present invention relates to a technique of obtaining a water-resistant ink image and reducing the phenomenon known as color bleeding in the formation of a color image on plain paper. The present invention particularly relates to a liquid composition to be used for image formation which employs an ink-jet system, to an ink set comprising a combination of the liquid composition and at least one ink, and to image forming methods and apparatus which use the liquid composition and the ink set.
2. Related Background Art
In an ink-jet recording system, recording is performed by ejecting ink droplets and adhering the ink droplets to a recording medium such as paper or the like. Particularly, in the methods disclosed in Japanese Patent Publication Nos. 61-59911, 61-59912 and 61-59914 in which bubbles are generated by applying thermal energy to an ink using an electrothermal converter as discharge energy supply means, and the bubbles are used to discharge ink droplets, a high density multi-orifice recording head can be readily manufactured and can record high-resolution and high-definition images at high speed.
However, since the ink used for conventional ink-jet recording generally comprises water as a main component, and a water-soluble high-boiling point solvent such as glycol for drying and preventing clogging of the nozzle, the method has the drawbacks that sufficient fixing properties cannot be obtained when recording on plain paper using such an ink, and that a nonuniform image is produced, possibly due to nonuniform distribution of loading material and sizing agent on the surface of a recording sheet. Furthermore, in the case of color recording, when a plurality of color inks are successively superimposed on a sheet before one of the color inks is fixed to the recording sheet, there is the problem that a satisfactory image cannot be obtained due to color bleeding or nonuniform mixing at the boundary between images having different colors. (This phenomenon is referred to as "bleeding" hereinafter.)
To enhance the fixing properties, therefore, Japanese Patent Laid-Open No. 55-65269 discloses a method of adding a compound for increasing penetrability, such as a surfactant, to an ink. Japanese Patent Laid-Open No. 55-66976 discloses a method of using an ink comprising a volatile solvent as a main component. However, although the method of adding a surfactant or the like to the ink increases the penetrability of the ink into the recording paper and improves the fixing properties of the ink and decreases bleeding to some extent, the method also causes the problem of decreasing the image density and chroma due to deep penetration of the ink's coloring material into the recording sheet. The method also causes lateral spreading of the ink and consequently causes the problem of decreasing the edge sharpness or resolution. On the other hand, since the latter means of using an ink comprising a volatile solvent as a main component not only produces the same problems as the former method but also readily produces clogging of the recording head nozzle due to the evaporation of the solvent, it is undesirable.
Methods of adhering a liquid to a recording medium before ejection of the ink in order to improve image quality have been proposed for solving the aforementioned problems.
For example, Japanese Patent Laid-Open No. 63-60783 discloses a method of recording with an ink containing an anionic dye after adhering a liquid containing a basic polymer to recording paper, and Japanese Patent Laid-Open No. 63-22681 discloses a method of recording an image by mixing a first liquid containing a reactive chemical species and a liquid containing a compound having reactivity to the reactive chemical species on a recording medium. In addition, Japanese Patent Laid-Open No. 63-29971 discloses a method of recording with an ink containing an anionic dye after adhering a liquid containing an organic compound having at least two cationic groups per molecule to a recording medium. Japanese Patent Laid-Open No. 64-9279 discloses a method of recording with an ink containing an anionic dye after adhering an acid liquid containing succinic acid or the like to the recording medium.
Further, Japanese Patent Laid-Open Nos. 64-63185 and 64-69381 disclose a method of recording with an ink after applying a liquid which makes the dye insoluble.
However, since all of the above methods have been proposed for suppressing bleeding of an image and improving water resistance by depositing dyes themselves, these methods do not sufficiently prevent the above-described bleeding between different color inks. In addition, since the deposited dyes are liable to be distributed nonuniformly on the recording sheet, the formed image has poor coverage of the pulp fibers of the recording sheet, thereby reducing the uniformity of the image.